perf: move PouchDB/IndexedDB operations to a Web Worker

All database reads and writes now run off the main thread via a
dedicated worker, eliminating IndexedDB overhead from the frame budget.

- Create data.worker.ts exposing the Data class via Comlink
- Refactor data.ts to export a Comlink-wrapped proxy and a standalone
  generateId() pure function (workers can't expose sync methods cleanly)
- Update all 10 call sites to import generateId directly instead of
  calling data.generateId()

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/hooks/useBacklinks.hook.ts

@@ -2,7 +2,7 @@ import { useAsyncState } from "@vueuse/core"
 import { ComputedRef, onUnmounted, toValue } from "vue"
 
 import { backlinkEventBus } from "@/bus/backlinkEventBus"
-import { data } from "@/data/data"
+import { data, generateId } from "@/data/data"
 import { DataType } from "@/data/DataType.enum"
 import { BacklinkNote } from "@/modules/note/models/BacklinkNote"
 
@@ -11,7 +11,7 @@ export const useBacklinks = (sha: string | ComputedRef<string>) => {
 
   const { state: backlink, execute } = useAsyncState(
     data.get<DataType.BacklinkNote, BacklinkNote>(
-      data.generateId(DataType.BacklinkNote, sha)
+      generateId(DataType.BacklinkNote, sha)
     ),
     null,
     {